MVHR Acoustic Distribution Boxes

[Johnny Jekyll]

We are deep in the design stage of our MVHR system, and the wife has been very clear that it's got to be quiet when running.

With that I'm currently looking at acoustic distribution boxes. Are they worth it?

I've seen some members on here making their own, but do they need to be specifically designed / sized?

Would purchasing new like the Airflow Airflex ones at BPC be a better way to go? Are there other better models? Things to look out for?

Any advice much appreciated thanks everyone.

[joe90]

Well I made mine and it works great, ply box lined with acoustic foam. I had heard that noise can be generated by the room terminals so I made my “throttling” within the distribution box and unless on boost completely quiet and only just able to hear it on boost.

[Johnny Jekyll]

Thanks @joe90 couple of questions on this if I may.

1 ) Presume that's one side for supply and one side for extract?

2 ) Did you build it to a specific design size or literally make a simple airtight ply box lined with acoustic foam? If so is bigger or smaller better?

3 ) How did you attach the big (125mm) ducting this side and the 75mm radial ducting the other side?

Thanks very much.

[joe90]

1/ yes

2/ I built it purely to accommodate the various pipes.

3/ MVHR came with adapters to fix the 125mm pipes to the ply, the 75mm was simply a tight and silicone .

[Conor]

The key to a quiet system is big ducts and big fans running at low rpm. Prevent noise being made, rather than trying to treat noise.

 

Attenuators / silencers help a lot as well, we've one on each main duct leaving the mvhr. The only noise we have is in the two bedrooms closest to the unit, despite a large attenuator and large semi rigid ducts. I'm going to dial back the airflow as I think it's too much. It's only noticeable on boost.

[SteamyTea]

  On 18/10/2022 at 17:32, Conor said:

The only noise we have is in the two bedrooms closest to the unit

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Do you get cross-talk between rooms?

Been known to be a problem with air ducted systems.

[JohnMo]

The distribution box - plenum chamber cancels out any cross talk.

[Conor]

  On 18/10/2022 at 18:45, SteamyTea said:

Do you get cross-talk between rooms?

Been known to be a problem with air ducted systems.

Expand  

No, only a couple locally branched ducts, most are single ducts from the manifolds. The semi rigid ducts seem really good at dampening sound.

[Johnny Jekyll]

  On 18/10/2022 at 15:52, joe90 said:

1/ yes

2/ I built it purely to accommodate the various pipes.

3/ MVHR came with adapters to fix the 125mm pipes to the ply, the 75mm was simply a tight and silicone .

Expand  

 

Thanks very much @joe90

[Johnny Jekyll]

A further question if I may. The folks at Vent Axia, Airflow and BPC all say the following general comments:

 

A smaller unit running on low speed should be quieter than a larger unit running on the same low speed.

A larger unit running on low speed will be quieter than a smaller unit running on higher speed.

Common sense fan noise I guess.

 

I've had some system designs put together and I'm learning all the time. I already know my MVHR unit location and all the duct runs. But the design help at this stage before committing is of course limited (understandably so).

 

I'm installing the system myself for the most part, so are there any tools or threads I can use / learn from to do a bit of system design myself / calculate volume and pressures / swapping models and items in and out, before proceeding further with a supplier?

 

Thanks

[Savage87]

Johnny I have done exactly what you are doing, I designed and installed my own MVHR, used different parts from different suppliers and it's all OK. When you first turn it on, for a couple of day you will hear it, unless it's on it's lowest setting but you(your wife) will get used to it and ignore it.

In my case I would have had the next size unit just so I can run it at a lower setting and be able to use more boost when needed.

 

Good luck!

 

Edited October 19, 2022 by Savage87
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